1. Field of the Invention
The present invention relates to the field of loop antennas, and more particularly to adjustable wristband loop antennas for wristworn receiving devices.
2. Description of the Prior Art
Recent advances in miniaturization of receiver components have made possible the development of wristworn receiving devices, such as wristworn pagers. Various antenna configurations have been developed using loop antennas which have been located within the wristband of the wristworn receiving device. Examples of such wristband antennas are as follows. U.S. Pat. No. 4,754,285 issued to Robitaille and U.S. Pat. No. 4,769,656 issued to Dickey illustrate loop antennas suitable for use in expansion type wristbands. U.S. Pat. No. 4,713,808 issued to Gaskill illustrates a basic wristband loop antenna configuration, which presumably requires retuning for different wrist sizes. U.S. Pat. No. 4,922,260 issued to Gaskill illustrates a wristband loop antenna which presumably must be cut to adjust the length and the corresponding resonance of the antenna to fit the wearer's wrist. U.S. Pat. No. 4,977,614 issued to Kurcbart illustrates an apparatus for adjusting the length of a single segment loop antenna while automatically compensating for the antenna tuning. And U.S. Pat. No. 4,873,527 issued to Tan illustrates a combination ferrite loop and wristband loop antenna arrangement. Such antennas, as described above, are generally suitable for use only at lower operating frequencies, such as below approximately 170 Megahertz. As the operating frequency is increased, such loop antennas can become more difficult to tune, become more directional, and become more difficult to provide an impedance match to the RF amplifier. There is a need to provide a wristband loop antenna structure which is capable of overcoming the deficiencies described above for operating at frequencies in excess of 170 Megahertz.